The adherence of oral streptococci to oral soft tissues and to the tooth surface appears to involve highly specific mechanisms for host recognition and bacterial cell adherence. Studies in this laboratory suggest that carbohydrate-binding proteins (lectins) on the streptococcal cell surface specifically bind to oligosaccharides present in glycoproteins and glycolipids on the surface of host cells in the salivary glycoproteins of the dental pellicle. Adherence of Streptococcus mutans involves a somewhat modified version of this adherence mechanism since this organism synthesizes an adherent polysaccharide, dextran, from sucrose of the host diet and specifically binds to this polysaccharide, resulting in attachment of bacterial cells to the host tooth surface. Several dextran-binding proteins have been isolated from S. mutans. These include a lectin, two forms of dextransucrase and three minor proteins not yet identified. Continuing research is directed to the characterization of these streptococcal proteins and analyses of their roles in adherence of S. mutans. Additional studies will be directed to the identification, purification and characterization of lectins from several other oral streptococcal species and identification of the host carbohydrates involved in adherence of these organisms to host oral tissues and the dental pellicle. Proteins binding salivary mucin (bovine) have been isolated from a strain of Streptococcus sanguis and currently are being characterized.